Noncorrosive lubricating oil



Patented Oct. 18, 1938 UNETE NONCORROSIVE LUBRICATING OIL Franz Rudolf Moser, Amsterdam, Netherlands, assignor to Shell Development Company, San Francisco, Calif., a corporation of Delaware No Drawing.

Application July 14, 1937, Serial No.

153,519. In the Netherlands July 24, 1936 8 Claim.

This invention relates to corrosion inhibitors of the type of alkyl succinic acids suitable for blending with lubricating oils, and to lubricating oils containing these inhibitors.

6 In my co-pending application, Serial No. 12,247, flied March 21, 1935 now issued as Patent No. 2,124,628 of July 26, 1938, of which the present case is a continuation-in-part, I have disclosed that certain polycarboxylic acids of relatively 10 .high molecular weights, such as voltolized oleic acid, agaric acid, alkenyl succinic acids, etc., when added to corrosive lubricating mineral oils, have the property of substantially suppressing their corrosiveness. While it was originally be- 5 lieved that this protective action extended to all metals, it was later found that certain metals, particularly the lead bronzes which are used as bearing metals in the construction of internal combustion engines, are, in some cases, insufficiently protected by many of the inhibitors.

It is a purpose of this invention to describe a type of corrosion inhibitors which gives substantially complete protection even to those metals which are attacked by corrosive lubricants in spite of the presence of the high molecular weight parboxylic acids disclosed in the beforementioned co-pending application; and it is another purpose to produce safe lubricating oils which possess positive anti-corrosive properties, improved oili- 80 ness and at least normal resistance to sludge formation, oxidation or breakdown by cracking upon use as crankcase oils in internal combustion engines.

Corrosiveness of mineral lubricating oils may have a number of causes. It may be due to the presence of corrosive substances in the oil, as sulfur compoundsQfree mineral or lower fatty acids, etc. Or it may be due to an inability to afford sufficient protection toward the action of air, carbon dioxide and water owing to the absence of natural corrosion inhibitors. Thus, solvent extracted lubricating oils, for instance, frequently exhibit pronounced corrosiveness which is probably caused by the removal of natural corrosion inhibitors during the refining by extraction. Lubricating distillates from certain crudes, as Venezuelan crudes, may be corrosivebecause of a content of corrosive sulfur compounds. Noncorrosive crankcase oils may become corrosive during use, when burning high sulfur fuels, due to formation of sulfuric acid; or hydrogen halides may be liberated and enter' the crankcase oil when burning leaded fuels containing organic halides. Again, corrosiveness may develop by decomposition of added oiliness or extreme pressure compounds, such as chlorinated organic compounds; or simply by oxidation of hydrocarbons to lower fatty acids.

O f the various polycarboxylic acids which possess improved corrosion inhibiting properties, alkylated succinic acids are especially valuable. I now have discovered that the effectiveness of alkylated succinic acids in the matter of inhibiting corrosion depends largely on the size of the alkyl chain or chains. As a general rule the larger these chains are, the greater is the protective ability of the succinic acid.

Alkylated succinic acids are most readily prepared by condensing maleic acid anhydride with individual olefines or mixtures of olefines, particularly mono-olefines. The resulting alkenyl succinic acid anhydrides are then hydrated to liberate the free succinic acids, which may be used as such for blending with the lubricating oil or which may first be hydrogenated to produce the saturated alkyl succinic acids. An illustrative method of preparing these substances is set forth in the Eichwald Patent 2,055,456. The term alkyl succinic acids as herein used refers to both the unsaturated as well as the saturated products obtained when condensing maleic acid anhydride and olefines, hydrating the product to liberate the free acids, and hydrogenating the latter, if desired.

In order to produce alkyl succinic acids which effectively protect lead bronzes used in the inanufacture of bearings, it is necessary to use in the condensation reaction olefines boiling not below 250 C., and preferably above 300 C. If olefines boiling below 250 C. are used, corrosive lubricating oils containing the normally required amounts of the resulting alkyl succinic acids, produce on lead bronzes a green scale, which in extreme cases may develop into severe pitting. If on the other hand the olefines boil above 250 C. no substantial green scale is formed, and when using olefines boiling above 300 C., the green scale fails to form altogether.

As to the upper boiling limits of suitable olefines there appear to be no critical limitations affecting the ability to prevent corrosion of the alkyl succinic acids produced therewith. However, it is desirable that the olefines be capable of distillation without substantial decomposition for the purpose of purifying the olefines as well as of separating unreacted olefines from the succinic acids produced therewith. In general therefore I prefer that the normal end boiling points of the distillate fractions be not greatly in excess of 400 C. Most olefines normally boiling below about 400 C. can be distilled readily, if not under normal, then under reduced pressures, without noticeable decomposition.

In addition to the ability of preventing green scale on lead bronzes, the higher alkyl succinic acids also afford a greater protection against the corrosion taking place in machinery, which is not in use over varying periods of time. This particularly applies to internal combustion engines, such as airplane motors which are ,frequently laid up for long periods. It is well known that when such engines are stored, especially after having been used, they are subject to internal corrosion, which may seriously injure cylinders, pistons, piston rings and other accurately machined parts of the engine. I have found that the relatively high alkyl succinic acids prevent corrosion of this type to a greater degree than the lower homologues over equal periods of time, and also hold incipient corrosion in abeyance for much longer periods.

Furthermore, besides giving a far greater protection against various types of corrosion, alkyl succinic acids produced with relatively high boiling olefines are capable of materially improving the oiliness of the oil to which they are added. Thus when testing oils containing alkyl succinic acids produced with low or high boiling olefines in the Boerlage four-ball apparatus described in Engineering July 14, 1933, pages 4647, for the purpose of determining the temperatures at which the oil films break under given operating conditions, so as to create direct metal to metal contact allowing an electrical current to pass and resulting in scoring of the rubbing test surface, it is found that the higher alkyl succinic acids always have considerable higher breakdown temperatures.

A further advantage of the higher alkyl succinic acids over the lower homologues lies in the ability of the former to reduce the coefiicients of friction of lube oils, to which they are added, to lower values over the entire temperature range up to their respective breakdown temperatures.

Suitable olefines to be used in the condensation reaction with maleic acid anhydride may be produced by cracking a heavy oil preferably in the vapor phase under conditions to yield maximum amounts of the desired high boiling olefines. Or else low boiling olefines may be polymerized to yield higher boiling olefines. Of particular usefulness are the normal olefines obtained in the vapor phase cracking of wax at temperatures around 550 to 560 0., although branched olefines may be used.' The olefines may be of either primary or secondary or tertiary type.

The condensation reaction is carried out by digesting maleic acid anhydride with the desired olefines or olefine fraction at an elevated temperature, preferably 150 to 250 C., and if desired in the presence of a mild condensing agent.

The quantities of the high alkyl succinic acids produced with olefines boiling above 250 C., re-

quired eifectively to prevent corrosion, vary depending upon the type of corrosion and its cause, and the type of metal to be protected. In all instances, however, less than 5%, and in most instances, less than l% has proven sufficient.

The following comparative example, demonstrating the influence of size of the alkyl chain in the alkyl succinic acids, serves to illustrate my invention.

300 parts of a distillate fraction of vapor phase cracked wax, boiling between 280 to 340 0., having a bromine number of 36 and an olefine content of about 60%, were heate. in an autoclave with 33 parts of maleic acid anhydride for two hours at 220 C. The product of reaction was subjected to a vacuum distillation to separate unreacted distillate and small amounts of maleic acid anhydridefrom the condensate. 97 parts of a residue were obtained having a saponification number of 345. This residue was then hydrated with an amount of water corresponding to the saponification number for one hour vat- 0., whereby the anhydrides were converted to the free acids. All parts were by weight.

,4 of the free acids so produced, added to a corrosive lubricating oil, completely prevented formation of green scale on lead bronze bearings of internal combustion engines.

Similar acids were then prepared by condensing maleic acid anhydride with a distillate fraction of a vapor phase cracked wax boiling between 160 and 200 C., vacuum distilling the product and hydrating the residue as before. of the acids so obtained, dissolved in the same corrosive lubricating oil used in the previous test, failed to prevent the green scale on the ,lead bronze bearing under the same test conditions. Upon prolonged exposure the scale developed into severe pitting.

When comparing the above lubricating oil blends in the Boerlage four-ball machine, under various pressures it was found that the breakdown temperatures of the oil film containing the higher acids were regularly about 50 C. higher than those of the blend containing the lower acids.

Entirely identical results, both as regards prevention of corrosion of lead bronze bearings and as regards breakdown temperature in the fourball machine, were obtained when using a product obtained by hydrogenation of the aforesaid condensation product having a saponification number of 345, the hydrogenation being carried out by subjecting 98 g. of the condensation product in an autoclave of 200 cm in the presence of a nickel-kieselguhr catalyst, to an initial hydrogen pressure of 100 atmospheres and a maximum temperature of 123 C., until the pressure remained constant, and hydration of the resulting hydrogenation product.

I claim as my invention:

1. A lubricant capable of preventing corrosion in internal combustion engines, consisting essentially of a mineral lubricating oil and containing a small amount of an alkyl succinic acid comprising a hydrated condensation product of maleic acid anhydride and an olefine boiling above 2. A lubricant capable of preventing corrosion in internal combustion engines, consisting essentially of a mineral lubricating oil and containing a small amount of an alkyl succinic acid comprising a hydrated condensation product of maleic acid anhydride and an olefine boiling between 300" and 400 C.

3. A lubricant capable of preventing corrosion in internal combustion engines, consisting essentially of a mineral lubricating oil and containing a small amount of an alkylene succinic acid comprising a hydrated condensation product of maleic acid anhydride and an olefine boiling above 250 C. I

4. A lubricant capable of preventing corrosion in internal combustion engines, consisting essentially of a mineral lubricating oil and containing less than 5% of an alkyl succinic acid comprising a hydrated condensation productof maleic acid anbydride and an oleiine boiling above 5. A lubricant capable oi preventing corrosion in internal combustion engines, consisting essentialiy o! a mineral lubricating oil and containing less than 1% of an alkyl succinic acid comprising a hydrated condensation product of maleic acid anhydride and an oleiine boiling above 6. A lubricant capable of preventing corrosion in internal combustion engines, consisting essentially of a mineral lubricating oil and containing a small amount oi ahydrated condensation product of maleic acid anhydride and an oleflnic hydrocarbon distillate boiling above 250 C.

'1. A lubricant capable of preventing corrosion a mans nunom mosmz. 

